Electronic image sensors are typically comprised of pixel arrays of a large number of very small light detectors, together called xe2x80x9cpixel arraysxe2x80x9d. These sensors typically generate electronic signals that have amplitudes that are proportional to the intensity of the light received by each of the detectors in the array. Electronic cameras comprise imaging components to produce an optical image of a scene onto the pixel array. The electronic image sensors convert the optical image into a set of electronic signals. These electronic cameras typically include components for conditioning and processing the electronic signals to allow images to be converted into a digital format so that the images can be processed by a digital processor and/or transmitted digitally. Various types of semiconductor devices can be used for acquiring the image. These include charge couple devices (CCDs), photodiode arrays and charge injection devices. The most popular electronic image sensors utilize arrays of CCD detectors for converting light into electrical signals. These detectors have been available for many years and the CCD technology is mature and well developed. One big drawback with CCD""s is that the technique for producing CCD""s is incompatible with other integrated circuit technology such as MOS and CMOS technology, so that processing circuits and the CCD arrays must be produced on chips separate from the CCD""s.
Another currently available type of image sensors is based on metal oxide semiconductor (MOS) technology or complementary metal oxide semi-conductor (CMOS) technology. These sensors are commonly referred to as CMOS sensors. CMOS sensors have multiple transistors within each pixel. The most common CMOS sensors has photo-sensing circuitry and active circuitry designed in each pixel cell. They are called active pixel sensors (APS""s). The active circuitry consists of multiple transistors that are inter-connected by metal lines; as a result, this area is opaque to visible light and cannot be used for photo-sensing. Thus, each pixel cell typically comprises photosensitive and non-photosensitive circuitry. In addition to circuitry associated with each pixel cell, CMOS sensors have other digital and analog signal processing circuitry, such as sample-and-hold amplifiers, analog-to-digital converters and digital signal processing logic circuitry, all integrated as a monolithic device. Both pixel arrays and other digital and analog circuitry are fabricated using the same basic process sequence.
Small cameras which utilize CCD arrays to convert an optical image to an electronic image have been commercially available for many years. Also, attempts have been made to produce small visible light cameras using CMOS sensors on the same chip with processing circuits. One such attempt is described in recently issued U.S. Pat. No. 6,486,503.
Small cameras using CCD sensors consume large amounts of energy (as compared to cameras with CMOS sensors) and require high rail-to-rail voltage swings to operate CCD. This can pose problems for today""s mobile appliances, such as Cellular Phone and Personal Digital Assistant. On the other hand, small cameras using CMOS sensors may provide a solution for energy consumption; but the traditional CMOS-based small cameras suffer low light sensing performance, which is intrinsic to the nature of CMOS APS sensors caused by shallow junction depth in the silicon substrate and its active transistor circuitry taking away the real estate preciously needed for photo-sensing.
U.S. Pat. Nos. 5,528,043 5,886,353, 5998,794 and 6,163,030 are examples of prior art patents utilizing CMOS circuits for imaging which have been licensed to Applicants"" employer. U.S. Pat. No. 5,528,043 describes an X-ray detector utilizing a CMOS sensor array with readout circuits on a single chip. In that example image processing is handled by a separate processor (see FIG. 4 which is FIG. 1 in the ""353 patent. U.S. Pat. No. 5,886,353 describes a generic pixel architecture using a hydrogenated amorphous silicon layer structure, either p-i-n or p-n or other derivatives, in conjunction with CMOS circuits to for the pixel arrays. U.S. Pat. Nos. 5,998,794 and 6,163,030 describe various ways of making electrical contact to the underlying CMOS circuits in a pixel. All of the above US patents are incorporated herein by reference.
Combining CMOS and MOS sensors with external processors can result in complexity and increase production costs. A need exists for improved camera technology which can provide cameras with cost, quality and size improvements over prior art cameras.
The present invention provides a novel MOS or CMOS based active sensor array for producing electronic images from electron-hole producing light. Each pixel of the array includes a layered photodiode for converting the electron-hole producing light into electrical charges and MOS and/or CMOS pixel circuits located under the layered photodiodes for collecting the charges. The present invention also provides additional MOS or CMOS circuits in and/or on the same crystalline substrate for converting the collected charges into images. The layered photodiode of each pixel is fabricated as continuous layers of charge generating material on top of the MOS and/or CMOS pixel circuits so that extremely small pixels are possible with almost 100 percent packing factors. In a preferred embodiment the sensor is a 0.3 mega pixel (3.2 mmxc3x972.4 mm, 640xc3x97480) array of 5 micron square pixels which is compatible with a lens of {fraction (1/4.5)} inch optical format. In a preferred embodiment the sensor along with focusing optics is incorporated into a cellular phone camera or a camera attachment the cellular phone to permit transmission of visual images along with the voice communication. In preferred embodiments all of the camera circuits are incorporated on or in a single crystalline substrate along with the sensor pixel circuits. The result is an extremely low cost camera at high volume production which can be made extremely small (e.g., smaller than the human eye). High volume production costs for the above 0.3 mega-pixel camera are projected to be less than $10 per camera.